It would be asking a lot of any actor to carry almost an hour of prime-time television on their own, but not Peter Capaldi.

Doctor Who

Last week’s episode "Face The Raven" saw the Doctor (Peter Capaldi) beaten and bested. Having been separated -- for good -- from his long-standing companion, Clara (Jenna Coleman), the Doctor began Saturday’s installment separated from his TARDIS; teleported into an obscure castle filled with dead ends, dungeon-like chambers, and the odd marauding Grim Reaper-look-alike monster. Over the course of the next hour, the truth slowly dawns on the Time Lord: this is a prison, or perhaps, his own personal hell. Suddenly, the farting aliens and ooh-er-missus innuendos of the Russell T. Davies era seem very far away.

To my knowledge, "Heaven Sent" is the first episode since the 1976 Tom Baker serial "The Deadly Assassin" to feature the Doctor traveling without a companion. This throws up some obvious narrative problems. Firstly, there is no one to play against, meaning that the story format plays us false whenever the character's required to emote; how one reacts to a locked door, an open window, or a word drawn in the dirt when alone is completely different to how one reacts in company. Secondly, when it comes to explaining what is going on, the usual characters who would wind up asking the audience’s questions for us -- the companion, the guest star, and so forth -- are not present, making exposition problematic.

Even without these constraints, it would be asking a lot of any actor to carry almost an hour of prime-time television on their own, but not Peter Capaldi. He’s simply incandescent in this episode, delivering what could in inexperienced hands sound like clunky expository lines with verve and urgency. The dining room scene -- a not-so-subtle nod to David Bowman’s (Keir Dullea) final meal in Kubrick’s 2001: A Space Odyssey (1968) -- is a tour de force: doing nothing more remarkable than sitting eating at the end of a bare table, surrounded only by plates and implements, Capaldi looks so exceptionally lonely that one’s heart goes out to him. Like Bowman, the Doctor is trapped in a liminal space, neither dead nor quite alive.

But is the story up to scratch? Seen from one perspective, "Heaven Sent" represents another addition to the by now very substantial pile of closed loop time travel stories of the Steven Moffat era. It has all of the showrunner’s usual hallmarks. It puts the protagonist in the tightest of spots, only to prise him out again thanks to plot contrivances of the "with one bound Dick was free" sort; there are the usual nods to the show’s mythology (as well as -- rather less satisfyingly -- borrowings of ideas from other Moffat vehicles, such as the "mind palace" trope from Sherlock); and it cleaves to ambiguity and shuns closure. Most importantly, it delights in the tyranny of predeterminism: for this is a prison in which the Doctor is doomed to play out the same events over and over again, and from which he will never, ever escape.

At least, that’s the terrible truth we are left to wrestle with for a good 10 minutes towards the show’s conclusion. And what a despairing 10 minutes it is. Part of the reason "Heaven Sent" works so wonderfully is that the Doctor, who in the post-2005 series has exhibited traits and abilities uncomfortably close to those of your average superhero, suddenly and unexpectedly assumes the characteristics (well, some of them, anyway) of a mere mortal. Early on in the episode, he confesses that he feels fear, alone in a castle with no way out, an extraordinary admission from a being for whom the word "invulnerable" might almost have been coined. Later, as the length of time for which he will be incarcerated becomes clear, one is left to ponder the fact that, sooner or later, the Doctor will run out of regenerations and die there.

The quality of the script is shown off to best effect by some masterful direction by Rachel Talalay. The episode calls for extraordinary directorial resources, including some fairly intricate CGI, underwater scenes, and point-of-view footage. Talalay pulls off all three beautifully, using fisheye lenses to convey the point of the view of the hulking, shuffling, pain-inducing monster prowling in the Kafka-esque corridors of the castle, and skillfully portraying the Doctor’s emotional dependency on Clara during the imagined TARDIS scenes. The editing is mesmerising, particularly towards the end, when dizzying, ever-faster cutting lends the Doctor’s epoch-spanning suffering virtue and grace.

Speculation has been rampant for months now that Moffat is thinking of leaving the show. To some, especially those who feel Doctor Who has become too self-referential and fan-orientated for its own good, such news would be just the ticket. Similarly, there are others who find the direction in which Moffat has taken the show rather indulgent. So many concepts central to the show’s existence have been retroactively explained away or otherwise modified to the showrunner’s own ends that, to them, they threaten to (depending on who you speak to) overwhelm its core values, or undermine its narratological integrity, or simply make it boring to watch, that it’s hard to think that these viewers would similarly feel anything but joy at hearing of his going. To them, the Steven Moffat era has been anathema.

On the strength of episodes such as "Heaven Sent", history, one suspects, will be rather kinder. For all the cosy metatextual references to Sherlock, the ludicrous sonic sunglasses, and the recherché, folded-in-on-itself conceit of the plot, this is tight, densely layered storytelling: thought-provoking, intellectually stimulating, and emotionally compelling. Although Moffat’s tenure has quite rightly been criticised as having produced some very inferior episodes, the peaks have been truly magnificent. It’s sad to think it may well take his departure for some to appreciate his quality.

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